let alone

let alone  {conj. phr.}

1. Even less; certainly not. — Used after a negative clause.

I can't add two and two, let alone do fractions.

Jim can't drive a car, let alone a truck.

Compare: MUCH LESS, NOT TO MENTION.

2. let alone or leave alone  {v.}

To stay away from; keep hands off; avoid.

When Joel gets mad, just let him alone.

Little Patsy was warned to leave the birthday cake alone.

Compare: LET BE.